The present invention relates to a non-insulating DC--DC converter for use in an electric vehicle, and more particularly, to a non-insulating DC--DC converter for use in charging a low-voltage battery with power from a high-voltage battery.
FIG. 7 shows an example of a conventional non-insulating DC--DC converter.
The non-insulating DC--DC converter shown in FIG. 7 comprises an input terminal 1b and an output terminal 7a. A check diode 12, a MOSFET 2, and a choke coil 4 are connected in series between the input terminal 1b and the output terminal 7a.
In addition, a diode 3 and a capacitor 5 are connected in parallel between the input terminal 1b and the output terminal 7a. The input terminal 1b has a battery terminal 1a for a high-voltage battery 1 connected thereto via an input cable 1c.
A control circuit 6 has a terminal connected to the high-voltage battery 1, a terminal connected to a gate of the MOSFET 2, and a terminal connected to one end of the capacitor 5. The output terminal 7a is connected to a low-voltage battery 7.
In such a configuration, the control circuit 6 applies a pulse voltage to the gate of the MOSFET 2 to control on/off operation of the MOSFET 2 in such a manner that a power from the high-voltage battery 1 is charged into the low-voltage battery 7.
In addition, if the control circuit 6 fails and provides an overvoltage to one end of the capacitor 5, the MOSFET 2 is turned off to prevent an output of the overvoltage. Furthermore, the inflow of an overcurrent is hindered by the check diode 12.
In the above conventional non-insulating DC--DC converter, however, if the MOSFET 2 is damaged due to an overvoltage or another reason, an overcurrent from the high-voltage battery 1 flows into the inside of the non-insulating DC--DC converter via an input cable 1c. When this occurs, the input cable 1c may be damaged by heat or the internal elements in the non-insulating DC--DC converter may be damaged, both of which are problems.
In addition, if an electronic equipment is connected to the non-insulating DC--DC converter, the internal elements in the electronic equipment may be damaged.
Furthermore, if the input cable 1c is connected to the negative-terminal side of the battery 1 as shown by the dotted line in the drawing, a reverse current from the low-voltage battery 7 may damage the MOSFET 2 and the check diode 12.
Furthermore, if the low-voltage battery 7 side is reversely connected, a reverse current from the low-voltage battery 7 causes a short-circuit current to flow via the diode 3, which may be damaged.
In addition, if the high-voltage battery 1 side is reversely connected, a short-circuit current may flow via the diode 3 to damage the MOSFET 2 and the check diode 12.
The present invention is provided in view of the above problems, and is intended to provide a non-insulating DC--DC converter that can prevent the internal elements from being damaged due to overvoltage or overcurrent, thus providing an appropriate power supply while also restraining costs.